Hi I am currently using NX client and also I am remotely accessing networking lab.I accidently turned off eth0 and I could not login to any of the hosts in the virtual networking lab.Whenever I try to enter command
ssh april
It always says
ssh: connect to host april port 22: No route to host
Can you please tell how can I turn it(ethernet) ON again.

How did you turn it off? Without network you need to use the console (to switch it on)

We are asked to to shut down a network interface of one host and try to reach the down interface from another host in order to get an ICMP destination unreachable message.
First I am remotely log in to host summer
and using command sudo ifconfig eth0 down
I turned it off and closed the window.
Now I am unable to connect to any host and I cannot turn it ON

does this host have another network card? if not, you need to open a console, but it depends on the config.

First: Please use a sensible thread title. most people posting need help.

Second: This isn't urgent. We're all volunteers here.

About your question: If this is the only network device on that host someone needs to physically go to that host, log into it and bring the network card back up.

Thanks for your reply.
Yes the host has another network card.

So you can either try that card to reach host or do what druuna suggested.

I am working on NX client and writing script.The problem is that I have a host and two IP addresses are assigned to that host one is 192.168.0.9(eth0) and another is 172.16.1.3(eth1). the default gateway of host is 172.16.1.5. There is one more router whose 172.18.1.3.(eth2)Now the problem is If you force a packet (to be routed by the default route) from a machine connected to 172.16.1.3 to be sent to machine connected to network 172.18.1.3 then that machine will
receive this packet from interface eth2 and forward the received packet to 172.16.1.5 through the same interface eth2. In this case that machine send sends 172.16.1.3 an ICMP redirect
message.

Adding to the same problem above ,I als want to know how can change the contents of routing table of host